Michael Davis
Preparing a mushroom substrate is the first step in growing mushrooms. The substrate is the
| Characteristics | Values |
|---|---|
| Purpose | To provide the essential nutrients and environment for mushrooms to grow and thrive |
| Key Criteria | Nutrient-rich, well-aerated, and free from contaminants |
| Common Substrates | Straw, wood chips, sawdust, paper, cardboard, coffee grounds, corn stalks, banana leaves, coco-coir, manure, wood-based mixes, grain |
| Preparation | Add water, additional nutrients, and sterilize or pasteurize |
| Sterilization/Pasteurization Methods | Boiling, oven method, hot water pasteurization, chemical treatment, fermentation |
| Container Options | Mason jars, small containers, buckets, plastic bags |
| Inoculation | Mix broken pieces of mycelium-covered grain (grain spawn) into the substrate |
| Moisture | Proper hydration is critical to successful colonization; too much or too little water can impact growth and contamination |
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What You'll Learn
Choose the right substrate for your mushroom type
Choosing the right substrate for your mushroom type is critical to your success in mushroom cultivation. Different species of mushrooms have different substrate preferences, and some are more particular than others, only producing high yields when grown on a specific substrate.
Some mushroom types, like oyster mushrooms, can grow on a wide range of substrates, including straw, cardboard, and even coffee grounds. Straw is, in fact, the most common substrate for oyster mushroom cultivation. For this substrate, cut straw into three- or four-inch pieces, then soak them in hot water. You can also add supplements like gypsum or coffee grounds to enhance the nutrient content.
For growing shiitake mushrooms, eucalyptus sawdust and wheat bran are commonly used. The size of the sawdust particles is important: if it's too fine, it will get waterlogged, and if it's too coarse, there will be too much airspace between particles, affecting your yields.
For common button mushrooms and portobella mushrooms, composted manure is used as the substrate. This involves a two-phase composting and sterilization process, where large piles of compost (manure and straw) naturally heat up to 160 degrees Fahrenheit, and beneficial organisms proliferate.
Gourmet mushrooms like Chanterelles or Morels may require specialized substrates, often involving a mixture of organic materials.
Other possible substrates include wood chips, paper, corn stalks, and agricultural waste products like coffee grounds and banana leaves.
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Prepare the substrate by adding water and nutrients
The first step in preparing a mushroom substrate is to choose the right base material. This can be straw, sawdust, wood chips, or even coffee grounds—all of which provide essential nutrients for mushroom growth. Straw is a popular choice due to its availability, affordability, and ability to hold moisture. However, it is important to ensure that the straw is free of fungicides, which can inhibit mushroom growth.
Once you have your base material, you will need to cut or shred it into small pieces, usually around 2 to 4 inches in length. This increases the surface area for mycelium colonisation, promoting healthy mushroom growth. After cutting, the straw should be pasteurised by submerging it in hot water, typically between 150 and 185 degrees Fahrenheit, for about an hour. This process eliminates contaminants and prepares the straw for mushroom growth.
The next step is to add water to your substrate. If using straw, soak it in water until it is fully hydrated and expanded. For other materials, such as coffee grounds and sawdust, simply mix them with water until you achieve a moist but not dripping consistency. Aim for a moisture content of around 60% to 70%.
Supplemental nutrients can also be added to the substrate to provide additional benefits for mushroom growth. Wheat bran or rice bran are common choices, providing extra nutrients like nitrogen. Other nutrient-rich additives include gypsum, which helps maintain pH balance, and vermiculite or coco coir, which improve aeration and moisture retention.
Finally, it is important to sterilise your substrate to ensure any remaining contaminants are eliminated. This can be done by heating the substrate to temperatures above 120 degrees Celsius, or even higher—above 250 degrees Fahrenheit—for complete sterilisation. This process kills off any competing mould or bacteria, giving your mushrooms the best chance to thrive.
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Pasteurise or sterilise the substrate
Before inoculating your mushroom substrate with spores or mycelium, it's important to pasteurise or sterilise it. This step kills off any competing mould or bacteria and gives your desired mushroom species the best chance of taking hold. It also helps to minimise the risk of mould and bacteria growth, giving your mycelium a head start.
Pasteurisation
Pasteurisation aims to kill most harmful microbes but leaves some beneficial ones intact. It is commonly used for substrates like straw, wood-based mixes, or cardboard. To pasteurise straw, cut it into three- or four-inch pieces. Then, either:
- Submerge it in water and heat it to 160-170°F for one hour on a stovetop (for indoors).
- Or, for outdoors, use a 55-gallon drum, a wire mesh basket, and a butane burner to pasteurise a whole bale of straw.
For cardboard, shred it into small pieces and soak them in hot water for 30 minutes. Drain the water and mix with a small amount of coffee grounds or straw for added nutrients.
Sterilisation
Sterilisation is a more intense process, eliminating all microbial life. This method is often used for nutrient-rich substrates like grain or composted manure. Sterilisation can be done by:
- Boiling your substrate in water for at least 30 minutes.
- Using a pressure cooker.
- Baking your substrate on a baking sheet in the oven at 300°F for about an hour.
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Inoculate the substrate with spawn or spores
Inoculation is the process of introducing spawn or spores to the substrate to initiate mushroom growth. This process typically involves mixing broken-up pieces of mycelium-covered grain (spawn) into the substrate.
Before inoculation, it is crucial to ensure that the substrate is properly hydrated. Straw, for instance, is usually hydrated during the pasteurization process by soaking it in hot water. For supplemented sawdust fruiting blocks, water should be mixed into the sawdust before sterilization. The substrate should be moist but not waterlogged, as this can lead to contamination.
For straw substrates, there are several inoculation methods. One method involves pasteurizing the straw by heating it to 160-170°F for about an hour. This can be done indoors by submerging the straw in a pillowcase or nylon mesh bag in water on a stovetop. Outdoors, a 55-gallon drum, wire mesh basket, and butane burner can be used to pasteurize a whole bale of straw. After draining the straw, it can be inoculated with grain spawn on a clean surface wiped down with 70% isopropyl alcohol.
Another method for straw substrates involves hot water pasteurization and lime water treatment. The straw is soaked in lime water for 2-4 hours, drained, and then immediately inoculated with spawn. This method treats about 20 kg of straw per batch of lime water.
Additionally, straw can be soaked in a peroxide solution (1 liter of 3% peroxide to 1 gallon of water) for 24 hours. After draining and rinsing with fresh water twice, the straw should be immediately inoculated with spawn.
For shiitake mushrooms, eucalyptus sawdust and wheat bran are commonly used as a substrate. The sawdust should be aged and consist of a mixture of coarse and fine particles to ensure proper aeration and prevent waterlogging. The substrate can then be inoculated with spawn or spores.
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Maintain the right hydration and humidity levels
Maintaining the right hydration and humidity levels is crucial for successful mushroom cultivation. Mushrooms require a moist substrate to grow, but too much water can encourage bacterial growth and inhibit full colonisation. Therefore, it is important to achieve the right balance.
The specific water requirements vary depending on the type of substrate used. For straw, hydration typically occurs during the pasteurisation process, where the straw is soaked in hot water. The straw can be submerged in water and heated to 160-170 degrees Fahrenheit for about an hour. Alternatively, a hot water pasteurisation method can be used, where the straw is soaked in lime water for 2-4 hours, followed by a rinse and a 24-hour soak in a peroxide solution.
For supplemented sawdust fruiting blocks, water should be mixed into the sawdust before sterilisation. The texture of the sawdust is important, as very fine sawdust can become waterlogged, while coarse sawdust may have too much airspace and be difficult to pack. A "squeeze test" is recommended to determine if the substrate has the right amount of hydration, also known as field capacity.
The humidity in the air also needs to be considered to prevent the substrate from drying out. Commercial growers often pack the substrate into large clear plastic bags, while home growers may use smaller containers like mason jars or buckets. The choice of container can impact the humidity levels and should be selected carefully.
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Frequently asked questions
A mushroom substrate is the "'soil" for your fungi. It is the medium that provides the essential nutrients and environment for mushrooms to grow and thrive.
Common mushroom substrates include straw, wood chips, sawdust, paper, cardboard, coffee grounds, and agricultural waste products.
First, select the right substrate for the specific type of mushroom you want to grow. Then, add water and any additional nutrients to the substrate. Next, process the substrate by sterilization or pasteurization to kill off any competing mold or bacteria. Finally, inoculate the substrate with mushroom spores or spawn to start the growing process.
Sterilization is a more intense process that eliminates all microbial life, while pasteurization aims to kill most harmful microbes while leaving some beneficial ones intact. Sterilization is often used for nutrient-rich substrates, while pasteurization is commonly used for straw or wood-based mixes.
The recommended way to test the hydration level of your substrate is by performing a squeeze test. The substrate should be properly hydrated during preparation, as too much or too little water can impact the growth of your mushrooms.
